G.O. Sars, 1883
Generic diagnosis:
The eye is round.
The peduncle of the 1st antenna is thicker in the male than in the female (Nyctiphanes-). Its 1st segment carries, distally and dorsally, an upward directed or somewhat backward directed lappet (leaflet) which differs between sexes (Nyctiphanes-lappet). The 3rd peduncular segment in the male is roundly convex on its outer lateral margin and concave on its inner margin (Nyctiphanes- ).
A rostrum is lacking. The frontal plate is an obtuse trough-like trianglar plate with raised margins.
Thoracic legs 1-6 are similar (Nyctiphanes-thoracic legs). The 7th leg is nearly as long but consists of only 2 segments. The 8th leg is minute and non-setose. Exopods of the 6th-8th legs are lacking in the female, except, at least, in N. australis which occasionally has an exopod on leg 6 (Baker et al., 1990); attention has not been given to other Nyctiphanes species in this respect.
The male petasma has the inner lobe serrated along the outer margin. The proximal and terminal processes are lacking. The median lobe is reduced, and the lateral process is long and only slightly curved, extending near to the end of the inner lobe.
A thelycum is present in fully mature females (Guglielmo and Costanzo, 1983). Eggs are shed into paired glutinous sacs attached to the posterior thoracic legs. (Spermatophores have not been observed attached to the female. Fertilization may occur within the external egg-sac; Einarsson, 1945).